DocBook XML validation

[Daniel Carrera <dcarrera math toronto edu>]

Hello,
I'm still trying to get the DocBook XML right.  I've made progress, but
some errors still elude me.  I'm using xmllint to test the XML.

Summary of errors (details in the PS):
1)  When I don't use the --valid flag, xmllint complains that mdash; is
not defined.
2)  When I use the --valid flag, the above error disappears, but I get
errors over <graphic> (which it thinks should be an empty tag) and
<artheader> (which it thinks does not exist).

Does anyone know what's going on?  and how to fix these?
I thought I read somewhere that <graphic> had been deprecated, but I can't
find the page anywhere.  I don't know what to use instead.

Thanks in advance,
Daniel.